IPC::Connection::Identifier is error prone and convoluted - Is not movable, leaks easily - Needs multi platform ifdefing at the call sites - Is represented by IPC::Attachment in .messages.in (should be IPC::Connection::Identifier or something like IPC::ConnectionHandle)
<rdar://problem/92318812>
Pull request: https://github.com/WebKit/WebKit/pull/4629